Maximal Network Rank
To solve the problem, we will take the following approach:
 Create a list of size
n
calleddegree
to keep track of the number of roads connected to each city.  For each road in
roads
, increase the degree of both cities (as roads are bidirectional).  Find the maximum network rank by iterating through all pairs of cities. The network rank between two cities is the sum of their degrees. But if there’s a road directly between the two cities, we need to subtract 1 (to avoid counting it twice).
 Keep track of the maximum network rank encountered.
Here’s the solution:


The logic behind subtracting 1 when two cities are directly connected is to avoid counting that road twice, as it’s directly connected to both cities.
Identifying Problem Isomorphism
“Maximal Network Rank” involves finding two cities that have the highest total number of connections, considering that if both cities are directly connected, that connection only counts once.
An approximate isomorphic problem to this is “Friends Of Appropriate Ages”. In this problem, instead of cities and their connections, you are dealing with ages of people and potential friendships, where the friendships must obey certain rules. Both problems involve working with connected entities and finding an optimal pair, but the contexts and specifics differ.
A simpler version could be “Number of Islands”. This problem involves working with a grid, and identifying connected components (the islands), which is a more straightforward task than the others mentioned.
A more complex problem is “Network Delay Time”, where, in addition to finding connections, there’s also a factor of time and signal propagation to consider. It adds another layer of complexity to the problem of assessing network connections.
These problems deal with the theme of connections between entities, whether those entities are cities, people, or points in a network. But they differ in the specifics of how these connections are defined and assessed.
10 Prerequisite LeetCode Problems
For “1615. Maximal Network Rank”, the following are a good preparation:
“1334. Find the City With the Smallest Number of Neighbors at a Threshold Distance”  This problem also focuses on understanding the network structure of cities, which is a key concept in the target problem.
“743. Network Delay Time”  Solving this problem will help you understand how to traverse networks and how different paths can impact the result.
“787. Cheapest Flights Within K Stops”  This problem can help you better understand how to deal with connections and paths within a network.
“210. Course Schedule II”  This problem involves handling prerequisites that can be likened to the connections in the target problem.
“399. Evaluate Division”  It helps in understanding how to use graph connections to calculate ratios, similar to how network ranks are calculated in the target problem.
“332. Reconstruct Itinerary”  This problem involves tracing a path through a network, similar to the network of cities in the target problem.
“207. Course Schedule”  Solving this problem helps understand prerequisites and ordering, akin to understanding connections between cities.
“684. Redundant Connection”  This problem involves finding unnecessary connections, which can improve your skills in identifying key connections.
“261. Graph Valid Tree”  This problem tests the ability to determine if a graph is a valid tree, which will enhance understanding of network structures.
“959. Regions Cut By Slashes”  This problem helps in understanding how connections (or slashes) can divide a network into distinct parts.
These cover how networks are structured and traversed, skills that are crucial for solving “1615. Maximal Network Rank”.
Problem Classification
This problem belongs to the domain of Graph Theory, specifically focusing on undirected graphs representing a network of cities and roads.
What Components
 Cities: There are
n
cities that form the nodes of the graph.  Roads: The bidirectional roads connecting the cities are represented as edges of the graph.
 Network Rank: A metric defined for pairs of cities as the total number of directly connected roads to either city (counting shared roads only once).
 Maximal Network Rank: The task is to find the highest network rank among all pairs of different cities.
Primary Classification
 Graph Theory: The main structure of the problem is a graph where cities are nodes and roads are edges.
Secondary Classifications
 Combinatorics: Finding all possible pairs of cities involves combinatorial aspects.
 Optimization: Finding the maximal network rank requires an optimization of the network rank function over the pairs of cities.
The problem describes a network of cities and roads, naturally mapping to a graph structure, hence Graph Theory is the primary domain. The roads are bidirectional, forming undirected edges in the graph. The network rank introduces a unique metric for evaluating the connectivity of pairs of cities, leading to a combinatorial and optimization problem as we must evaluate this metric over all possible pairs to find the maximal value. Therefore, the problem involves elements of graph traversal, combinatorial analysis, and optimization to arrive at the solution.
Clarification Questions
Clarification questions can help ensure a clear understanding of the problem and any specific constraints or requirements. Here are some possible questions one might ask regarding this problem:
 Uniqueness of Roads: Is it guaranteed that there is at most one road connecting any two cities, or can there be multiple roads between the same pair of cities?
 SelfConnected Cities: Are there any constraints preventing a city from being connected to itself?
 Input Constraints: Can the roads array contain duplicates? If so, how should they be handled?
 Output Requirements: Is there a specific format required for the output, or is a single integer representing the maximal network rank sufficient?
 Edge Cases: How should the edge case of no roads (empty roads array) be handled? Should the function return zero, or is there a different expectation for this case?
 Performance Constraints: Are there any specific performance constraints or expectations for the solution, given the constraints on
n
and the size of the roads array?  Definition of Network Rank: Is the definition of the network rank clear, especially how shared roads are counted only once for the pair of cities being considered?
 Graph Representation: Is there any preference for how the graph should be represented in code? Can standard graph data structures be used, or is there a specific format required?
 NonConnected Cities: The problem statement mentions that not all cities must be connected. Is there any further information on how disconnected components of the graph should be handled?
By asking these questions, one can gain a clear understanding of the problem’s requirements and constraints, ensuring that the implemented solution aligns with the problem’s expectations.
Problem Analysis and Key Insights
Analyzing the problem statement for finding the maximal network rank of the infrastructure gives us several key insights:
Bidirectional Roads: The problem defines roads as bidirectional, meaning that the connection between two cities is mutual. A road between city
a
and cityb
means that both cities are connected to each other.Network Rank Definition: The network rank of two different cities is defined as the total number of roads directly connected to either city. If a road is connected to both cities, it is counted only once. This definition is central to the problem.
Maximal Network Rank: The goal is to find the maximum network rank across all pairs of different cities. This requires examining every possible pair and calculating their network rank.
Graph Representation: The infrastructure can be represented as an undirected graph, where cities are nodes and roads are edges. This insight might guide the choice of algorithms or data structures to use in the solution.
Constraints: The constraints provided in the problem statement (e.g., number of cities, roads, no selfconnected cities, at most one road between any pair of cities) give us important boundaries that can guide the solution design and optimization.
Disconnected Cities: Not all cities must be connected, and there can be separate disconnected components within the graph. The problem is still solvable without complete connectivity between all cities.
Combination of Pairs: The problem essentially requires evaluating the combination of pairs of cities and assessing their network rank. This forms the core of the problemsolving approach.
Edge Cases: Consideration of edge cases like no roads or handling of duplicate roads (if any) may also be necessary based on the understanding of the problem.
These insights form the foundation of understanding the problem, allowing for the development of a strategy to solve it. By understanding the nature of the roads, network rank definition, graph representation, and specific constraints, one can identify the most suitable algorithms and techniques to apply.
Problem Boundary
The scope of this problem involves:
Understanding the Network Structure: Analyzing the given bidirectional connections between cities (nodes) and understanding the definition of network rank.
Evaluating Pairs of Cities: Investigating all possible pairs of different cities to calculate their network rank, considering that a road connecting both cities in a pair is counted only once.
Maximization Task: Finding the maximal network rank across all pairs, i.e., finding the maximum value of all the calculated network ranks.
Adhering to Constraints: Ensuring that the solution complies with the given constraints, such as the number of cities, the structure of the roads array, and the limitation that there is at most one road connecting each pair of cities.
Handling Disconnected Components: Recognizing that not all cities need to be connected, and the solution must still handle the disconnected parts of the infrastructure.
Optimization Considerations: Depending on additional requirements or specifications (not detailed in the problem statement), there may be considerations for optimizing the solution, especially if the problem needs to handle the upper bounds of the constraints.
Output Format: Returning the result as an integer representing the maximal network rank.
The problem doesn’t involve additional complexities like weighing roads, dynamic changes to the infrastructure, or other variations that could expand the scope. It’s focused on a specific calculation based on the given structure of cities and roads.
Establishing the boundary of this problem involves clearly defining the inputs, outputs, constraints, and specific rules or conditions that the solution must adhere to. Here’s how you can do that:
Inputs:
n
: An integer representing the total number of cities, where (2 \leq n \leq 100).roads
: An array of pairs representing the bidirectional roads between cities, where (0 \leq \text{{roads.length}} \leq n \times (n  1) / 2). Each pair contains two integers representing the cities connected by the road.
Output:
 An integer representing the maximal network rank of the entire infrastructure.
Constraints and Conditions:
 The roads are bidirectional.
 The integers in the pairs of roads are within the range (0) to (n1), and they are not equal to each other.
 There is at most one road connecting any given pair of cities.
 Not all cities have to be connected.
Specific Rules:
 Network rank is defined as the total number of directly connected roads to either city in a pair. A road that is directly connected to both cities in a pair is counted only once.
Exclusions:
 Aspects not mentioned or outside the defined constraints, such as weighing roads, dynamic changes in the network, additional properties of the cities, etc., are outside the boundary of this problem.
Optimization Considerations:
 Although not explicitly stated, efficiency in handling the upper bounds of the constraints may be an implied requirement.
By understanding and considering these elements, you create a boundary that defines what the problem encompasses and what it does not. It helps in forming a clear picture of what needs to be addressed in the solution and avoids overcomplicating or underestimating the problem.
Distilling the Problem to Its Core Elements
Fundamental Concept or Principle:
 This problem is based on the concept of graph theory. Specifically, it deals with finding the maximum degree of connectivity between vertices (cities) in an undirected graph (bidirectional roads).
Simplest Way to Describe the Problem:
 Imagine you have several cities, and some of them are connected by roads. The task is to find two cities that have the most number of roads connected to them. If there’s a road connecting these two specific cities, count it only once.
Core Problem to Solve:
 The core problem is to find the maximum network rank, i.e., the highest number of roads connected to any two different cities in the entire infrastructure. Simplified: Find the two cities that, together, have the most connections to other cities.
Break Down the Problem into Key Components:
 Identify the cities (vertices) and the roads (edges) and represent them in a suitable data structure.
 Calculate the number of connections for each city.
 Identify the pair of cities that have the maximum combined connections.
 Consider the direct connection between these two cities, if any.
Minimal Set of Operations:
 Initialization: Prepare a data structure to store the number of connections for each city.
 Calculate Connections: Iterate through the roads and increment the connection count for each city involved.
 Find Maximum Combined Connections: Iterate through the cities and find the pair with the highest combined connections, adjusting if a direct connection between the pair exists.
 Return Result: Return the maximal network rank as the solution.
By understanding these aspects, you can formulate a clear and concise solution that focuses on the essential elements of the problem without overcomplicating the process.
Visual Model of the Problem
Visualizing the problem statement can help in understanding the core concept and how to approach the solution. For this particular problem, a graph would be an excellent way to visualize it. Here’s how you might do it:
Cities as Vertices: Treat each city as a vertex or node in the graph. If there are ’n’ cities, you will have ’n’ vertices.
Roads as Edges: Treat the roads as edges connecting the vertices. Since the roads are bidirectional, the graph is undirected. If there is a road connecting city ‘a’ and city ‘b’, draw an edge between the corresponding vertices.
Network Rank: The network rank of two different cities is the total number of edges (roads) connected to either city. If there is a road directly connecting those two cities, count it only once.
Example Visualization
Consider the example with n = 4
and roads = [[0,1],[0,3],[1,2],[1,3]]
.
You can visualize it as:
0  1
 \ 
 \ 
3  2
 Cities are labeled as 0, 1, 2, and 3.
 Lines between numbers represent roads connecting cities.
 In this example, the network rank of cities 0 and 1 is 4, as there are four roads connected to either 0 or 1, with the road between 0 and 1 counted only once.
Visualizing the problem in this way can provide a clear picture of the connections between cities and help guide your approach to solving the problem. You can see how each city connects to others and identify the pair of cities that have the maximal network rank.
Problem Restatement
You have ’n’ cities, and some of them are connected by roads. These roads are bidirectional, meaning you can travel both ways. The “network rank” of two different cities is calculated as the total number of roads connected to either of the two cities. If there is a direct road between those two cities, it’s only counted once.
Your task is to find the highest network rank among all possible pairs of different cities. In other words, you need to find the two cities that together are connected to the largest number of other cities (including each other) via direct roads.
Input:
 An integer ’n’ representing the number of cities (2 <= n <= 100).
 An array of roads, where each road is represented by a pair of integers [a, b] indicating a bidirectional road between cities ‘a’ and ‘b’ (0 <= a, b <= n1, and a != b). There can be at most one road between any pair of cities.
Output:
 The maximal network rank of the entire infrastructure, which is the highest network rank among all pairs of different cities.
The problem statement defines the structure of the cities and their connections and requires identifying the two cities that have the maximum combined connections, including each other’s connection if they are directly connected by a road.
Abstract Representation of the Problem
An abstract representation focuses on the underlying structure and relationships within the problem, removing any realworld context. Here’s an abstract formulation for the given problem:
Entities:
 Nodes: Represent cities.
 Edges: Represent bidirectional connections between nodes (roads).
Concepts:
 Network Rank: The sum of the degrees of two nodes minus any edge between them.
Problem:
 You have a graph with ’n’ nodes and a set of edges representing connections between these nodes.
 The task is to identify a pair of nodes whose network rank is maximized.
 The network rank of two nodes ‘a’ and ‘b’ is defined as the sum of the degrees of ‘a’ and ‘b’, minus 1 if there is an edge between ‘a’ and ‘b’. The degree of a node is the number of edges connected to it.
Input:
 An integer ’n’ representing the number of nodes.
 A list of edges, represented as pairs of connected nodes.
Output:
 The maximal network rank within the graph.
By representing cities as nodes and roads as edges, we transform the problem into a graph theory problem, focusing on the degrees of the nodes and relationships between them, rather than the realworld concepts of cities and roads.
Terminology
Node: In the context of this problem, a node represents a city. The graph consists of ’n’ nodes, each representing an individual city within the infrastructure.
Edge: An edge represents a road between two cities (nodes). Since the roads are bidirectional, the connections between nodes are also bidirectional.
Degree of a Node: The degree of a node in a graph is the number of edges connected to it. In this problem, it represents the number of roads connected to a particular city.
Graph: A graph is a mathematical representation consisting of nodes (vertices) and edges that connect pairs of nodes. In this problem, the graph represents the entire infrastructure of cities and roads.
Bidirectional Graph: A graph where all edges are twoway. If there is an edge from node A to node B, there is also an edge from node B to node A. In this problem, all roads connect cities in both directions, so the graph is bidirectional.
Network Rank: A specific concept in this problem, the network rank of two different cities, is defined as the total number of directly connected roads to either city. If a road is directly connected to both cities, it’s counted once. In graph terms, it’s the sum of the degrees of the two nodes, minus 1 if there is an edge between them.
Maximal Network Rank: The highest network rank among all pairs of different cities (nodes) within the infrastructure. The task is to find this value.
These specialized terms and concepts are essential for understanding the problem as they form the structural and logical foundation of the problem statement. Understanding them helps in conceptualizing the problem in terms of graph theory, which aids in problemsolving and implementation.
Problem Simplification and Explanation
Imagine you have a big toy set with different towns (cities) and toy roads connecting them.
Towns (Cities): Picture each town as a dot or a point on your play mat. You can have as many towns as you like!
Roads: Now, you can connect these towns with toy roads. Some towns have more roads connected to them, and some have fewer. You can even have roads that connect two towns directly to each other.
Friendship Score: Think of the roads as a way for two towns to be friends. The more roads a town has, the more friends it has. If two towns have a road directly connecting them, they are special friends.
Best Friendship Pair: You want to find the two towns that together have the most friends, but if they are special friends (have a road directly connecting them), you only count that road once. This is like finding the two people in your class who together know the most people but don’t count their friendship twice.
Max Friendship Score: Your task is to find the highest friendship score among all pairs of towns. It’s like finding the two best friends in your class who together know the most people.
Metaphor: Think of this problem like a big friendship game in your school. The towns are the students, the roads are their friendships, and the goal is to find the two students who together have the most friends without doublecounting if they’re friends with each other.
By understanding the towns, roads, and friendships, you’re trying to find the best pair of towns in your toy set that have the most connections to others. It’s a fun game of connections and friendships!
Key Concepts
 Cities: These are the distinct locations in the network.
 Roads: The connections between cities. A road between two cities is a bidirectional link.
 Network Rank: The total number of direct connections (roads) to a city. If two cities are directly connected, that road is counted only once for the pair.
 Maximal Network Rank: The highest network rank across all pairs of different cities.
Metaphor
Imagine the cities as people at a party, and the roads as handshakes between them. The network rank of two people is the total number of handshakes they have with others, but if they’ve shaken hands with each other, you only count that handshake once. The maximal network rank is finding the two people at the party who together have shaken hands with the most people.
Interaction of Concepts
 Cities (People): Distinct points that can be connected.
 Roads (Handshakes): Connections between cities, representing relationships.
 Network Rank (Handshake Count): Sum of connections for a pair of cities, counting a direct link between them only once.
 Maximal Network Rank (Most Social Pair): Finding the pair of cities (people) with the highest combined number of connections (handshakes).
By understanding these key concepts and the metaphor of a party with handshakes, the problem becomes a social puzzle: finding the two most socially connected people in a room, considering all the handshakes but not doublecounting if they’ve shaken hands with each other.
Constraints
Let’s explore specific characteristics or conditions that can be utilized to develop an efficient solution.
Limited Number of Cities: The constraints specify that the number of cities (n) ranges from 2 to 100. This limitation allows us to use simple data structures like arrays to manage city connections.
Direct Road Connections: Roads are bidirectional, meaning that a road from city A to city B is the same as a road from city B to city A. This simplifies calculations as we only have to consider a road once.
Unique Road Connections: There is at most one road connecting any pair of cities. This ensures that we don’t have to consider multiple paths between two specific cities.
Maximal Network Rank Calculation: Since we are calculating the maximal network rank across all pairs of different cities, we can keep track of the number of connections for each city. By iterating through all possible pairs, we can find the sum of connections for each pair and subtract one if there’s a direct road between the cities in the pair.
Use of Simple Counters: We can use an array or a similar data structure to keep track of the number of connections to each city. By going through the roads and incrementing the counters for both cities in each road, we’ll have the total number of connections for each city, facilitating the calculation of the network rank.
Linear Relationship Between Cities and Roads: Since the number of roads is directly related to the number of cities (0 to n * (n  1) / 2), iterating through the roads or performing actions based on the number of cities and roads will still result in a manageable computational complexity.
These characteristics can be leveraged to design an algorithm that iteratively calculates the network rank for each pair of cities and finds the maximum, without unnecessary complexity or redundant calculations. By taking advantage of these patterns and numerical ranges, an efficient solution can be devised.
Analyzing the constraints in this problem provides key insights that help in formulating an efficient solution:
Finite Number of Cities: With a maximum of 100 cities, the problem’s scale is manageable, allowing the use of simple data structures like arrays to store and manage information.
Finite Number of Roads: The constraint that there are at most ( n \times (n1) / 2 ) roads ensures that the problem can be solved without considering an exponentially large number of possibilities.
Bidirectional Roads: Since the roads are bidirectional, it simplifies the logic required to navigate between cities. This characteristic reduces the complexity of interpreting the connections between cities.
Unique Road Connections: With at most one road between any pair of cities, we donâ€™t have to handle multiple paths between the same two cities. This again simplifies the logic and reduces computational complexity.
Direct Calculation of Network Rank: The definition of network rank as the total number of directly connected roads to either city in a pair allows us to calculate the rank by simply counting connections. This direct relationship leads to a more straightforward algorithm.
Roads Are the Only Connections: Since the connections are exclusively defined by the roads, we do not need to consider other types of connections or relationships between the cities. This constraint keeps the problem domain narrow and focused.
By taking into account these constraints, we can tailor the solution specifically to the problem’s defined boundaries. It guides us in selecting appropriate algorithms, data structures, and techniques that align with the given conditions, leading to an efficient and streamlined solution.
Case Analysis
Here are several examples that cover a wide range of the input space. These examples include edge cases, boundary conditions, and typical scenarios to provide a comprehensive view of the problem:
1. Minimal Cities Case (Edge Case)
Input: n = 2, roads = [[0, 1]] Output: 1 Analysis: With only two cities and a single road between them, the maximal network rank is 1. This is the smallest possible scenario and serves as a base case for testing.
2. No Roads Case (Boundary Condition)
Input: n = 5, roads = [] Output: 0 Analysis: No cities are connected, so the maximal network rank is 0. This tests the handling of an absence of connections.
3. Complete Connection Case (Boundary Condition)
Input: n = 3, roads = [[0, 1], [0, 2], [1, 2]] Output: 3 Analysis: All cities are directly connected to each other, resulting in the maximal network rank for the given cities.
4. Single City with Multiple Connections (Typical Scenario)
Input: n = 4, roads = [[0, 1], [0, 2], [0, 3]] Output: 3 Analysis: One city is directly connected to all others. This example represents a common pattern and tests the ability to handle multiple connections from a single node.
5. Complex Network (Typical Scenario)
Input: n = 6, roads = [[0, 1], [1, 2], [2, 3], [3, 4], [4, 5], [5, 0]] Output: 4 Analysis: The cities form a circular network where the maximal network rank is between two cities connected to two other cities each. This highlights the handling of more intricate road patterns.
6. Duplicate Roads (Potential Pitfall)
Input: n = 3, roads = [[0, 1], [1, 2], [2, 0], [0, 1], [1, 2]] Output: 3 Analysis: While the problem states there’s at most one road connecting cities, this example tests how the implementation handles or prevents duplicate connections.
These examples, categorized by their unique characteristics, offer a comprehensive view of the problem. By analyzing each case, we can better understand the constraints, potential pitfalls, and key insights required to create a robust solution that handles all possible scenarios.
Visualizing these cases can help in understanding the problem better. Here’s how you can visualize the examples mentioned earlier:
1. Minimal Cities Case (Edge Case)
You have two cities with a single road between them.
A  B
2. No Roads Case (Boundary Condition)
You have five cities with no roads between them.
A B C D E
3. Complete Connection Case (Boundary Condition)
You have three cities, and each city is connected to every other city.
A
/ \
BC
4. Single City with Multiple Connections (Typical Scenario)
You have one city directly connected to all others.
A
/\
B C D
5. Complex Network (Typical Scenario)
You have six cities forming a circular network.
AB
/ \
F C
\ /
ED
6. Duplicate Roads (Potential Pitfall)
You have three cities with duplicate connections. This example is tricky since the problem statement specifies at most one road between cities, but you can visualize it like the complete connection case, understanding that duplicates may be ignored or handled separately.
A
/ \
BC
Visualizing these cases provides an intuitive understanding of the network’s structure and the relationships between the cities. It highlights how different configurations lead to different maximal network ranks, offering insights into the problem’s complexities and constraints.
Analyzing the different cases provides several key insights that are essential to understanding the problem:
Minimal Connectivity: In the minimal cities case, the maximal network rank is straightforward and easy to determine, as there is only one possible connection.
Lack of Connectivity: The no roads case highlights the importance of the presence of roads for the network rank calculation. It emphasizes that without roads, the network rank is zero.
Complete Connectivity: The complete connection case shows that connecting all cities to each other doesn’t necessarily lead to the maximal network rank for a pair of cities since the network rank is determined based on the total number of directly connected roads to either city.
Central Hub Connectivity: The single city with multiple connections case emphasizes the role of hub cities that can potentially contribute to a higher maximal network rank due to their connectivity with multiple other cities.
Circular and Complex Networks: Complex network cases illustrate that the maximal network rank might be determined by not just a simple set of connections but how these connections are structured and distributed among the cities.
Handling Duplicate Roads: Analyzing potential pitfalls like duplicate roads ensures understanding of how to handle or ignore repeated connections since the problem statement specifies at most one road connecting a pair of cities.
Variety in Network Ranks: Different configurations can lead to different network ranks, demonstrating the need for an approach that can efficiently evaluate various scenarios to find the maximal network rank.
Symmetry in Connections: The bidirectional nature of the roads suggests that the connections are symmetrical, which can be leveraged in solving the problem.
By carefully studying these cases, we can recognize patterns, constraints, and characteristics that guide us in formulating an efficient solution strategy for finding the maximal network rank of the entire infrastructure.
Identification of Applicable Theoretical Concepts
The problem can be analyzed through several mathematical and algorithmic concepts that can help in simplifying or efficiently solving it:
Graph Theory: The problem can be represented as an undirected graph where cities are vertices and roads are edges. Techniques like adjacency lists or adjacency matrices can be used to store and manipulate the connections.
Degree of a Vertex: In graph theory, the degree of a vertex represents the number of edges incident to it. In this problem, the degree of a vertex corresponds to the number of roads connected to a city. Calculating and storing the degrees can help in determining the network rank of a pair of cities.
Combinatorics: Since the problem is about pairs of different cities, combinatorial concepts related to choosing pairs can be applied to iterate through possible city pairs without redundancy.
Maximization Techniques: The problem’s objective is to find the maximal network rank, and thus, concepts related to optimization and maximization can be employed.
Greedy Approach: A greedy strategy that focuses on pairs of cities with the highest individual degrees may lead to an efficient way to find the maximal network rank.
Dynamic Programming: By breaking down the problem and storing intermediate results, dynamic programming could be leveraged to avoid redundant calculations, especially in complex network structures.
Complexity Analysis: Analyzing the time and space complexity helps in determining the efficiency of the chosen algorithm, ensuring it falls within the constraints given the input size (2 <= n <= 100).
These mathematical and algorithmic concepts provide a foundation for designing an efficient solution to the problem, taking advantage of properties like symmetry, degrees of vertices, and the nature of the connections within the network.
Simple Explanation
Imagine you live in a land with several towns, and there are roads connecting some of these towns. You and your friend decide to go on an adventure to explore the towns and their connections.
You both come up with a game to make the adventure more exciting. You want to find two towns that have the most number of roads going in and out of them. But there’s a catch  if a road connects the two towns you picked, you only count it once!
Here’s a metaphor to make it simpler: Think of the towns as ice cream stands, and the roads as different flavors of ice cream connecting these stands. You and your friend want to find two ice cream stands that offer the most flavors. If there’s a unique flavor that connects both stands, you only count it once. The winner of the game is the one who picks the two stands with the most flavors.
In simpler terms, the problem is about finding two towns (or ice cream stands) that have the maximum number of connections (or flavors) to other towns. You want to explore and find these two towns to win the game or enjoy the most ice cream flavors!
Problem Breakdown and Solution Methodology
Let’s continue with our metaphor of ice cream stands and flavors, and break down the process of solving this problem into smaller steps:
Count the Flavors at Each Stand:
First, you’ll need to determine how many flavors (roads) are connected to each ice cream stand (town). Create a list or a chart where you note down how many connections each town has.
Find Shared Flavors Between Stands:
Next, you’ll want to find any flavors that are shared between two stands, i.e., roads that connect two towns directly. You’ll only count these once when calculating the total flavors for two stands.
Calculate the Total Flavors for All Pairs:
Now, you’ll calculate the total flavors for all pairs of ice cream stands. For each pair, you’ll add the flavors from both stands, subtracting one if they share a flavor. Keep track of the maximum total as you go along.
Find the Best Pair:
The pair of stands with the most total flavors is the answer to the problem. This will be the maximum network rank of the infrastructure.
Consider Changes in Parameters:
If you change the number of towns or roads, or the connections between them, it will affect the total flavors for the pairs, possibly changing the best pair.
Example
Imagine you have 4 ice cream stands with the following connections (flavors):
 Stand 0: connected to stands 1 and 3 (2 flavors)
 Stand 1: connected to stands 0, 2, and 3 (3 flavors)
 Stand 2: no connections (0 flavors)
 Stand 3: connected to stands 0 and 1 (2 flavors)
Using the above steps:
 Count flavors at each stand:
[2, 3, 0, 2]
 Find shared flavors: Stands 0 and 1 share one flavor, as do stands 1 and 3.
 Calculate total flavors:
 Stands 0 and 1: 2 + 3  1 (shared) = 4
 Stands 0 and 2: 2 + 0 = 2
 Stands 0 and 3: 2 + 2 = 4
 Stands 1 and 2: 3 + 0 = 3
 Stands 1 and 3: 3 + 2  1 (shared) = 4
 Stands 2 and 3: 0 + 2 = 2
 Find the best pair: The maximum total flavors is 4, so any pair with this total is a solution (stands 0 and 1, or 0 and 3, or 1 and 3).
So the answer is 4, and you’ve found the pairs of ice cream stands that let you taste the most flavors on your adventure!
Inference of ProblemSolving Approach from the Problem Statement
Here are the key terms and concepts in the problem and how they guide the approach to solving it:
Cities (n):
 Explanation: These represent the nodes in the network.
 Strategy: Knowing the total number of cities informs the size of the structures used to track connections (such as arrays or lists).
Roads:
 Explanation: The roads are bidirectional connections between two cities.
 Strategy: This defines the edges in the graph and indicates the relationships between cities. We must track these connections to calculate the network rank.
Network Rank:
 Explanation: This is the total number of directly connected roads to two different cities.
 Strategy: Calculating this requires summing the connections for each pair of cities, with consideration of shared connections. The approach involves using iterative methods to compute these values.
Bidirectional Road:
 Explanation: A road that connects two cities, and it’s counted only once if it’s directly connected to both cities.
 Strategy: Requires careful consideration of doublecounting connections when summing the roads for each city pair.
Maximal Network Rank:
 Explanation: The highest network rank among all pairs of different cities.
 Strategy: This necessitates maintaining a variable to keep track of the maximum network rank as we iterate through city pairs.
Constraints (size of n, uniqueness of roads):
 Explanation: These conditions define the bounds and limitations within which the solution must operate.
 Strategy: These guide the validation of inputs and optimization of the solution, ensuring it operates efficiently within the defined space.
Understanding these key terms and concepts informs the choice of data structures (like arrays to track city connections) and algorithms (iterative methods to calculate ranks) that will be used to create an efficient solution to the problem.
Recognizing properties through tables or diagrams can be a highly effective way to understand the relationships within the problem. Here’s how you can represent them:
Cities and Roads (Graph Representation):
 Diagram: Draw circles for cities (nodes) and lines for roads (edges).
 What It Shows: The connections between different cities and how roads link them.
 Benefit: Helps in visually recognizing which cities are connected and can be useful in understanding how to calculate network rank.
Network Rank (Table Representation):
 Table: Create a table with rows and columns representing cities. In each cell, you can place the network rank of the corresponding pair of cities.
 What It Shows: The network rank between each pair of cities.
 Benefit: Gives an organized view of network ranks and helps in easily finding the maximal network rank.
Bidirectional Roads (Enhanced Graph Representation):
 Diagram: Draw arrows on the lines connecting cities to represent the directionality of the roads.
 What It Shows: That each road is bidirectional and is counted once if it’s directly connected to both cities.
 Benefit: Helps in understanding how to avoid doublecounting roads in network rank calculation.
Maximal Network Rank (Highlighted Graph/Table):
 Diagram/Table: Highlight or color the pair of cities with the maximal network rank in the graph or table.
 What It Shows: The pair of cities that have the highest network rank.
 Benefit: Makes it easy to visually identify the solution.
By using these visual representations, you can better understand the structure of the problem and the relationships between the key concepts. Graphs will help in understanding the connections, while tables will help in organizing and analyzing the data. These tools can make both the problem and the solution more tangible and easy to work with.
Below are details for representations #2 and #4.
Network Rank (Table Representation):
You can create a table to represent the network rank between each pair of cities. This table could be structured as follows for the given example (n = 4, roads = [[0,1],[0,3],[1,2],[1,3]]):
0  1  2  3  

0    2  0  2 
1  2    1  2 
2  0  1    0 
3  2  2  0   
 Rows and columns represent cities.
 The value in a cell represents the total number of directly connected roads to either city of the corresponding pair. For example, the value 2 in cell (0,1) means there are 2 roads connected to either city 0 or city 1.
 Diagonal entries are left as ‘’ since a city cannot be paired with itself.
Maximal Network Rank (Highlighted Graph/Table):
Using the table above, you can highlight or color the cells with the highest network rank. In this example, the maximal network rank is 4, so you would highlight the corresponding cells.
0  1  2  3  

0    2  0  2 
1  2    1  2 
2  0  1    0 
3  2  2  0   
 The cells with the highest network rank are highlighted or bolded (in this case, 2).
 Note that these values would need to be combined with the corresponding values from the other city in the pair to calculate the total network rank. For example, the pair (0,1) would have a network rank of 2 + 2 = 4.
These visual representations can help you identify the relationships between cities and roads, and quickly determine the maximal network rank within the entire infrastructure.
Simple Explanation of the Proof
I’m having trouble understanding the proof of this algorithm. Could you explain it in a way that’s easy to understand?
Stepwise Refinement
Let’s break down the problem into detailed steps and identify granular actions, independent parts, and repeatable patterns.
1. Stepwise Refinement
 Initialize the Network Rank Table: Create an array to keep track of the number of roads connected to each city.
 Analyze Roads: Loop through the
roads
array and increment the network rank for each connected city.  Calculate Pairwise Ranks: Using the network rank for each city, calculate the network rank for every pair of different cities. Deduct one if both cities are directly connected.
 Find Maximal Network Rank: Determine the maximum network rank by iterating through all the pairwise ranks.
 Return Result: Return the maximal network rank.
2. Granular, Actionable Steps
 Initialize: Start with an array of zeros, of size equal to the number of cities
n
.  Analyze Roads:
 For each road [a,b], increment the value at index
a
andb
in the array.  If a road connects cities
a
andb
, keep track of this connection.
 For each road [a,b], increment the value at index
 Calculate Pairwise Ranks:
 Iterate through all possible pairs of cities.
 Sum the values at the corresponding indices in the network rank array.
 Deduct one from the sum if the cities are directly connected.
 Find Maximum: Keep track of the maximum value obtained in step 3.
 Return: Return the maximal network rank.
3. Independent Parts
 Analyzing Roads: This step is independent and can be parallelized. The roads can be processed separately to update the network rank for each city.
 Calculating Pairwise Ranks: Calculating the network rank for each pair is an independent operation, and these calculations can be done concurrently.
4. Repeatable Patterns
 Incrementing Network Rank: The pattern of incrementing the network rank for each city appears repeatedly throughout the list of roads.
 Calculating Pairwise Ranks: This step involves a consistent pattern of combining two cities’ ranks and checking for a direct connection.
By breaking down the problem into these detailed steps, you can effectively understand and implement a solution that finds the maximal network rank of the infrastructure.
Solution Approach and Analysis
Let’s break down the solution into a detailed stepbystep approach and illustrate it with an analogy and examples.
Step 1: Initialize the Network Rank Table
 Create an array of zeros, with size equal to the number of cities (n).
 Imagine the array as a scoreboard in a game where each city has a score of zero at the start.
Step 2: Analyze Roads
 For each road connecting cities a and b, increment the corresponding scores in the array.
 Think of each road as a connection in a social network, and the score represents how many friends (connections) each city has.
Step 3: Calculate Pairwise Ranks
 Iterate through all possible pairs of cities, summing their individual scores. If a pair of cities are directly connected by a road, deduct one.
 Imagine combining two people’s social network connections to see their combined influence, but not doublecounting mutual friends.
Step 4: Find Maximal Network Rank
 Find the maximum value among the pairwise ranks calculated in Step 3.
 This represents the pair of cities with the greatest combined influence.
Step 5: Return Result
 Return the maximal network rank.
Effect of Changes in Parameters
 If the number of cities (n) increases, the computational time will increase.
 If there are more direct connections between cities (more roads), the maximal network rank could be higher.
Example
Consider n = 4 and roads = [[0,1],[0,3],[1,2],[1,3]].
 Initialization: array = [0, 0, 0, 0]
 Analyze Roads: array = [2, 2, 1, 2]
 Calculate Pairwise Ranks: e.g., (0, 1) = 2 + 2  1 (since they are directly connected) = 3
 Other pairs: (0,2) = 3, (0,3) = 4, (1,2) = 3, (1,3) = 3, (2,3) = 3
 Find Maximal Network Rank: Max = 4
 Return Result: 4
This methodical approach ensures that the problem is solved efficiently, taking into account all connections between cities and identifying the pair with the maximal network rank.
Identify Invariant
An invariant is a property that remains unchanged throughout the execution of a program or algorithm. In the context of this problem, the invariant is related to the structure of the network and how we calculate the connections.
The invariant here can be stated as the following:
 The Degree of a City: At any point during the processing of the roads, the degree (number of connections) of a city
i
in the network is equal to the count of roads connected to that city. This invariant is maintained throughout the algorithm, as we increment the degree for each city whenever we encounter a road connected to it.
This property helps ensure that our calculations of the network ranks are consistent and accurate, as we build up the degrees for each city and then use them to calculate the combined degrees for pairs of cities. It acts as a stable foundation on which the rest of our calculations are based.
Identify Loop Invariant
An invariant is a property that remains unchanged throughout the execution of a program or algorithm. In the context of this problem, the invariant is related to the structure of the network and how we calculate the connections.
The invariant here can be stated as the following:
 The Degree of a City: At any point during the processing of the roads, the degree (number of connections) of a city
i
in the network is equal to the count of roads connected to that city. This invariant is maintained throughout the algorithm, as we increment the degree for each city whenever we encounter a road connected to it.
This property helps ensure that our calculations of the network ranks are consistent and accurate, as we build up the degrees for each city and then use them to calculate the combined degrees for pairs of cities. It acts as a stable foundation on which the rest of our calculations are based.
In the context of algorithms, an invariant is a condition that holds true before and after an operation or a sequence of operations, while a loop invariant is a specific type of invariant that holds true before and after each iteration of a loop.
In the problem statement described, if we are employing a loop to iterate through the roads and calculate the degrees of each city, the loop invariant would be the specific condition that holds true before and after each iteration of that loop.
In this case, the loop invariant could indeed be the same as the invariant described earlier: the degree of a city i
is equal to the count of roads connected to that city at any point during the iterations. This property remains true before and after each iteration of the loop that processes the roads, and it helps ensure the consistency and correctness of the algorithm as it builds up the degrees for each city.
So yes, in the context of this problem, the invariant and loop invariant can be the same, depending on how the solution is implemented.
Thought Process
Solving the problem of finding the maximal network rank of an infrastructure of cities connected by roads involves understanding the underlying structure and then applying specific steps to find the solution. Here are the essential steps:
Understand the Problem: The first step is to comprehend what is being asked. The maximal network rank of two cities is the total number of directly connected roads to either city.
Define the Connections: You’ll want to create a data structure that stores the number of roads connected to each city. This could be an array, where the index represents the city and the value represents the number of connected roads.
Iterate Through Roads: Loop through the given roads and increment the connections for the corresponding cities.
a. For each road
[ai, bi]
, increment the connections for cityai
and citybi
. b. The value at each city’s index will give you the number of roads connected to that city.Calculate Maximal Network Rank: Once the connections are tallied, you’ll need to calculate the network rank for every pair of cities and find the maximum.
a. Loop through the cities and combine the counts of connected roads for each pair. b. If a road is directly connected to both cities in a pair, decrement the sum by 1, as it’s only counted once. c. Keep track of the maximum network rank as you iterate through the pairs.
Return the Result: The maximal network rank calculated in step 4 is the final result.
Example
To illustrate the approach, let’s use the example provided earlier:
n = 4, roads = [[0,1],[0,3],[1,2],[1,3]]
 Create an array to store connections:
connections = [0, 0, 0, 0]
.  Iterate through roads:
 For
[0,1]
, incrementconnections[0]
andconnections[1]
.  Continue this pattern for all roads:
connections = [2, 2, 1, 2]
.
 For
 Calculate the maximal network rank:
 Pair (0,1): rank = 2 + 2  1 = 3 (since there is a common road between 0 and 1).
 Continue for other pairs, and find the maximum: 4.
 Return 4 as the result.
Insights
The thought process revolves around understanding the relationships between cities (represented by connections) and then applying straightforward counting and maximization logic. By breaking down the problem into these manageable steps and thinking about the underlying structure, the solution becomes clear and approachable.
Let’s build on the thought process and write the code to solve the problem.
Thought Process
 Understanding the Problem:
The problem asks us to find the maximal network rank, which is the maximum sum of directly connected roads between any two different cities.
Cues in the Problem Statement:
a. Each road connects two cities, meaning we need to account for connections to both cities. b. A road directly connecting two cities in a pair is only counted once, indicating a need for special handling for this case. c. The problem constraints (e.g., the number of cities and roads) allow for straightforward iteration.
Defining the Approach:
a. Count the connections for each city. b. Iterate through all pairs of cities to find the maximal network rank.
Insights
 The problem essentially requires us to model connections between cities.
 The constraints are simple enough that we don’t need a complex data structure like a graph; an array will suffice.
 Special handling is required for roads that connect both cities in a pair.
Code


This code first counts the connections for each city and then calculates the network rank for each pair of cities, keeping track of the maximum. The final result is the maximal network rank for the entire infrastructure.
Establishing Preconditions and Postconditions
Let’s analyze the method based on the provided sections.
1. Parameters
 Inputs:
n
(an integer representing the number of cities) androads
(a list of lists representing the roads between cities).  Types:
n
is an integer,roads
is a list of lists where each list contains two integers.  Representation:
n
represents the total number of cities, androads
represents the bidirectional connections between cities.
2. Preconditions
 State of the Program: No specific state is required.
 Constraints on Input:
2 <= n <= 100
0 <= roads.length <= n * (n  1) / 2
 Each road list
[a, b]
should satisfy0 <= a, b <= n1
anda != b
.  Each pair of cities has at most one road connecting them.
 Program State: Not applicable.
3. Method Functionality
 Expected to Do: The method is expected to calculate and return the maximal network rank of the entire infrastructure.
 Interaction with Inputs: It iterates through the roads and cities to calculate the network rank.
4. Postconditions
 State of Program: No change in the state of the program.
 Return Value: The method returns an integer representing the maximal network rank of the infrastructure.
 Side Effects: There are no side effects; the method does not modify any global state or input parameters.
5. Error Handling
 Response to Unmet Preconditions: The code doesn’t explicitly handle errors related to unmet preconditions. If the inputs do not meet the constraints (e.g., negative values, improper roads), the behavior of the code is undefined.
 Exception, Special Value, Other: The method does not throw exceptions or return special values for incorrect inputs. Additional validation could be added if necessary to handle incorrect inputs gracefully.
Problem Decomposition
Let’s assume we are solving a hypothetical problem involving the calculation of the maximal network rank of an infrastructure based on the number of cities and their connecting roads.
1. Problem Understanding
 Explanation: We are given
n
cities and a list of roads that connect them. We need to find the maximal network rank, which could be defined as the maximum total connections between any two cities.  Key Components: Number of cities (
n
), roads (list of connections between cities).
2. Initial Breakdown
 Major Parts: Understand the data structure, calculate the connections for each city, find pairs of cities with maximal connections.
3. Subproblem Refinement
 Understanding Data Structure:
 Represent cities and their connections.
 Calculating Connections:
 For each city, count its connections.
 Finding Maximal Pairs:
 Identify pairs of cities with the maximum total connections.
4. Task Identification
 Repeated Tasks: Counting connections for each city might be a repeated task.
5. Task Abstraction
 Abstracted Task: Create a function like
count_connections(city)
that returns the number of connections for a given city, making it reusable.
6. Method Naming
 Task Names:
represent_cities
,count_connections
,find_maximal_pairs
.
7. Subproblem Interactions
 Order of Performance: First, represent cities, then count connections, and finally find maximal pairs.
 Dependencies: Counting connections depends on representing cities properly; finding maximal pairs depends on counting connections.
By breaking down the problem into these stages, we can approach the solution in a methodical and logical manner, making the process of solving the problem more manageable.
From Brute Force to Optimal Solution
Let’s continue with the hypothetical problem of calculating the maximal network rank of an infrastructure based on cities and their connecting roads.
Brute Force Solution
A brute force solution could be to iterate through all pairs of cities, and for each pair, count the total number of connections (sum of connections for both cities minus the connection between them, if any), keeping track of the maximum found.
Pseudocode:


Inefficiencies:
 The main inefficiency is repeatedly summing connections for the same city.
 Time complexity is (O(n^3)) (as the sum inside nested loops takes (O(n)) time).
 Space complexity is (O(n^2)) (due to the adjacency matrix).
Optimization Process
Step 1: Reduce Repeated Work
Optimization: Store the connections for each city in a separate array, so we don’t have to recalculate it.
Pseudocode:


Improvement:
 Time complexity is reduced to (O(n^2)).
 The space complexity remains the same, (O(n^2)).
Step 2: Optimize Space Complexity
Optimization: Since we’re interested in only direct connections, we can use an adjacency list instead of a matrix.
Pseudocode:


Improvement:
 Time complexity remains (O(n^2)).
 Space complexity is reduced to (O(n + E)), where (E) is the number of roads.
Through these optimizations, we have significantly improved the time and space complexity of the brute force solution without losing the correctness of the approach.
Code Explanation and Design Decisions
Let’s break down the optimized code for the problem of calculating the maximal network rank of an infrastructure based on cities and their connecting roads, as discussed earlier:
1. Initial Parameters
n
: Represents the number of cities. It sets the boundary for the iterations and calculations.roads
: A list of road connections between pairs of cities. This is the main data that we need to interpret and manipulate.
2. Primary Loop or Iteration
 The nested loops
for i in range(n)
andfor j in range(i + 1, n)
iterate through all pairs of cities.  Each iteration represents an attempt to find the maximal network rank for a specific pair of cities.
 The iteration advances the solution by systematically exploring all possible pairs.
3. Conditions or Branches Within the Loop
 The condition
(1 if j in connections[i] else 0)
checks whether there is a direct connection between citiesi
andj
.  This condition signifies a need to adjust the rank if there is a direct connection between the pair of cities, as it should not be doublecounted.
4. Updates or Modifications to Parameters
rank
: Calculated for each pair of cities, it captures the total connections minus any direct connection between the pair.max_rank
: Updated with the highest rank found so far. This modification reflects changes in the state of the solution as we discover new potential maximal network ranks.
5. Invariant
 An invariant in this context is that the
connection_counts
array always accurately reflects the number of connections for each city, and theconnections
set accurately captures the connections between cities.  This invariant helps to ensure that the solution is accurately calculating the network rank for each pair of cities.
6. Significance of the Final Output
 The final output,
max_rank
, represents the maximal network rank in the given infrastructure.  It satisfies the problem’s requirements by identifying the largest possible network rank that can be obtained by considering all pairs of cities and their connecting roads.
The code’s structure and the logical flow have been designed to systematically approach the problem, ensuring that all possibilities are explored while taking into account the specific constraints and requirements of the problem domain. By maintaining clarity in the iterations, conditions, modifications, and invariants, the code is able to accurately and efficiently solve the problem, producing an output that aligns with the problem statement’s objectives.
Coding Constructs
Let’s dissect the code and its strategy to understand the different facets of the solution:
1. HighLevel ProblemSolving Strategies
 Iterative Analysis: Iterating through all possible pairs of cities to evaluate network rank.
 Optimization: Utilizing precomputed data to reduce redundant calculations.
 Maximization: Keeping track of the maximum network rank found.
2. Explanation to a NonProgrammer
 Imagine a country with various cities and roads connecting them. This code finds the two cities that, if their direct road was closed, would still leave the most roads connecting them to other cities. It’s like finding the most bustling pair of cities.
3. Logical Elements or Constructs
 Loops: For systematically exploring all pairs of cities.
 Conditions: For special handling when two cities are directly connected.
 Variables: Storing intermediate and final results.
 Arrays/Sets: Storing connections and counts.
4. Algorithmic Approach in Plain English
 Count how many roads connect to each city.
 Look at every possible pair of cities.
 For each pair, add the number of roads connecting to both but subtract one if they’re directly connected to each other.
 Keep track of the largest number found.
5. Key Steps or Operations
 Initialization: Set up data structures for connections and counts.
 Iteration: Go through all pairs of cities.
 Rank Calculation: For each pair, calculate the network rank considering direct connection.
 Maximization: Keep track of the largest rank found.
6. Algorithmic Patterns or Strategies
 Iterative Enumeration: Iterating through combinations of elements.
 Memoization: Using precomputed counts to avoid repeated calculations.
 Conditional Logic: Applying specific logic based on certain conditions (direct connection).
 Reduction: Reducing the problem to simple arithmetic operations and logical decisions.
By breaking down the code into these components and explaining them in the context of the problem’s requirements, we can see how the code utilizes standard problemsolving strategies and algorithmic patterns to arrive at the solution in an efficient and logical manner.
Language Agnostic Coding Drills
Let’s break down the code into distinct learning units or coding drills and then discuss the stepbystep problemsolving approach.
1. Dissect the Code into Distinct Concepts:
Here are the distinct coding concepts, abstracted from specific programming languages:
 Variables and Data Types: Understanding how to declare and use variables.
 Arrays and Lists: Storing and managing a collection of elements.
 Loops: Iterating through elements, either with a fixed number of iterations or based on a condition.
 Conditional Statements: Making decisions in code based on conditions.
 Functions: Creating reusable pieces of code.
 Arithmetic Operations: Performing basic arithmetic like addition, subtraction, multiplication, etc.
 Comparison Operations: Comparing values using less than, greater than, equal to, etc.
 Logical Operations: Using AND, OR, NOT, etc., to combine boolean expressions.
2. List Concepts by Difficulty:
 Easy:
 Variables and Data Types: Basics of any programming task.
 Arithmetic Operations: Fundamental mathematical operations.
 Intermediate:
 Arrays and Lists: Requires understanding of data structures.
 Loops: Conceptualizing iteration over elements.
 Conditional Statements: Introduces decisionmaking in code.
 Advanced:
 Comparison Operations: Involves understanding ordering and equality.
 Logical Operations: Combining conditions requires abstract thinking.
 Functions: Requires understanding how to modularize code.
3. ProblemSolving Approach:
Here’s the stepbystep process to build the final solution using these concepts:
 Understand the Problem: Analyze the problem statement and identify key components.
 Setup: Utilize variables and data types to store the input, and create arrays/lists to keep track of connections and counts.
 Iterate Through Pairs: Implement loops to iterate through all pairs of cities.
 Evaluate Conditions: Use conditional statements to handle the specific case where two cities are directly connected.
 Perform Calculations: Apply arithmetic operations to calculate the network rank for each pair of cities.
 Find Maximum Rank: Utilize comparison operations to keep track of the maximum rank found.
 Modularize: If needed, create functions to encapsulate reusable parts of the code, like calculating rank for a pair.
 Compile Results: Bring together the results to form the final solution.
By breaking down the code into these granular concepts and then sequentially building them up, learners can understand each piece of the puzzle separately and then see how they combine to form the complete solution. This approach promotes clear and thorough comprehension of both the problem and its solution.
Targeted Drills in Python
1. Coding Drills for General Concepts:
a. Variables and Data Types:


b. Arrays and Lists:


c. Loops:


d. Conditional Statements:


e. Functions:


f. Arithmetic Operations:


g. Comparison Operations:


h. Logical Operations:


2. ProblemSpecific Concepts and Drills:
In our case, there might not be any additional problemspecific concepts that are not covered by the general concepts already listed. The building blocks provided above should be sufficient to tackle the problem.
3. Integrating Drills to Solve the Problem:
By understanding the problem and carefully employing the drills described above, we can create a complete solution:
 Use variables and data types to set up initial parameters.
 Utilize arrays and lists to handle collections of elements.
 Implement loops to iterate through elements.
 Utilize conditional statements to add logical decisionmaking.
 Use functions to create reusable code.
 Implement arithmetic operations for calculations.
 Utilize comparison operations to compare values.
 If needed, use logical operations to combine conditions.
These individual drills can be thought of as modular building blocks that fit together, each contributing to the creation of the final solution. By using them in the right sequence and with proper connections, a complete solution can be built that is both efficient and maintainable.
Q&A
Similar Problems
The problem we’ve just solved involves graph traversal, counting connections, and calculating a specific metric based on those connections. Here are 10 problems that use similar underlying concepts:
547. Number of Provinces: This problem requires you to find the number of connected components in a graph, similar to counting connections between cities.
399. Evaluate Division: You need to construct a graph and traverse it to evaluate mathematical expressions, involving graph traversal concepts like the original problem.
207. Course Schedule: This involves detecting cycles in a directed graph, akin to understanding connections between nodes, much like our original problem of connecting cities.
721. Accounts Merge: This problem requires you to identify connected components in an undirected graph, related to counting direct connections between nodes.
684. Redundant Connection: You are asked to find an edge that, when removed, will leave the graph treeconnected, similar to our original problem’s concept of connectivity.
785. Is Graph Bipartite?: You must determine if a graph can be colored with two colors without adjacent nodes having the same color, similar to the concept of analyzing connections between nodes.
261. Graph Valid Tree: This problem asks whether a graph is a valid tree, which requires understanding connections between nodes and cyclic structures, much like in our original problem.
133. Clone Graph: Cloning a graph requires a deep understanding of graph traversal and connections between nodes, which relates to our problem’s need to understand city connections.
323. Number of Connected Components in an Undirected Graph: Similar to problem #1, this one also involves finding connected components in a graph, related to counting connections between cities.
734. Sentence Similarity: This problem requires you to determine if two sentences are similar by defining connections between words. Though not a graph problem, it still involves understanding connections, akin to the connections between cities in our original problem.